Device for therapeutical treatment of a blood vessel

ABSTRACT

The invention relates to a device for therapeutical treatment of a blood vessel. It comprises in combination a stent, a balloon catheter for the insertion of the stent into a blood vessel, and a generator for generating ultrasound. The stent can be expanded radially and is of such construction that it is caused to vibrate and/or develop heat when exposed to ultrasound. Inserted into the blood vessel the stent can be expanded by means of the balloon catheter to engage the inside surface of the blood vessel in order to be left in the expanded condition as an inside lining in the blood vessel after the balloon catheter having been withdrawn from the blood vessel. Energy is transferred wirelessly by means of ultrasound generated by the generator, from an extra-corporeal position to the stent as located in the blood vessel engaging the inside surface thereof.

The invention relates to a device for therapeutical treatment of a bloodvessel.

U.S. Pat. No. 5,078,736 describes a stent which can be introduced into ablood vessel by means of a balloon catheter and which can be expandedradially to engage the inside surface of the blood vessel in order thatthe stent after withdrawal of the balloon catheter from the blood vesselwill be left in the expanded condition thereof as an inside lining inthe blood vessel. The stent comprises an electrically conducting socketwhich can be heated when located in the blood vessel, by means of anextra-corporeally located power source in order to provide an intendedtherapeutic effect in the blood vessel.

In one embodiment this heating is effected inductively i.e. without wireconnection between the stent and the power source. Since the stent has asmall mass a powerful coil is, however, required for heating the stentto the necessary temperature inductively and it may even be necessary toallow the induction coil to operate at such a high power that watercooling thereof may be necessary, which makes the device expensive inmanufacture and also cumbersome in use.

The purpose of the invention is to provide a much more easily handleddevice for wireless external influence on the stent, and for thispurpose the invention provides a device of the kind referred to abovewith the features of claim 1.

The use of ultrasound for therapeutic purposes is known per se. E.g.GB-A-2 126 901 discloses an ultrasound hyperthermia applicator forheating relatively large tissue. volumes by ultrasound energy.

The invention also relates to a method for therapeutic treatment of ablood vessel comprising the steps of inserting a stent into the bloodvessel by means of a balloon catheter, expanding the stent by means ofthe balloon catheter to engagement with the inside surface of the bloodvessel, withdrawing the balloon catheter from the blood vessel, theexpanded stent being left in the blood vessel in engagement with theinside surface thereof, and exposing the stent left in the blood vesselto an extra-corporeally generated ultra-sound field in order to providea therapeutical effect in the blood vessel in the region of the stent.

In order to explain the invention in more detail an embodiment thereofwill be described below reference being made to the accompanyingdrawings in which

FIG. 1 is a partly broken away perspective view of the stent formingpart of the device according to the invention,

FIG. 2 is a side view of a balloon catheter forming part of the deviceand having a guide wire, and the stent said elements being shownseparated,

FIG. 3 is a side view of the balloon catheter with the stent applied tothe catheter for insertion into a blood vessel,

FIG. 4 is a side view of the balloon catheter under expansion of theballoon and the stent applied on the balloon,

FIG. 5 is a side view with portions broken away of the stent insertedinto the blood vessel,

FIG. 6 is an enlarged fragmentary cross-sectional view of the bloodvessel and the stent inserted therein, and

FIG. 7 is a fragmentary view of a human body with the stent insertedinto a coronary vessel the stent being affected by an ultrasound fieldgenerated extra-corporeally by the generator forming part of the device.

FIG. 8 is a perspective view of an example ultrasound generatorincluding multiple ultrasound transmitters mounted to a reflector.

The stent disclosed in FIG. 1 is indicated generally with 10 andcomprises a socket 11 of such kind that it can be expanded radially. Thesocket can comprise a netting or an axially slotted socket, and it canbe made of metal, e.g. stainless steel, or of plastic, e.g. a polymer.If the socket is made of plastic this can be cross-linked so that theplastic has a memory by which it assumes, at heating, a larger diameterthan that it had before heating. The socket can have a length of theorder of 0.5-10 cm, an inside diameter of the order of 1.0-15.0 mm, anda wall thickness of the order of a a tenth mm or two. The diameters haveto be adjusted to the blood vessel wherein the stent is to be used. Anexpandable heat insulating cover 12 is provided on the outside of thesocket 11, and this cover can consist of plastic, silicon rubber, graft,or the like. The stent can also be coated on the outside thereof and/oron the inside thereof with silicon rubber or graft, possibly with carbonpowder (carbon black) mixed therewith.

For application of the stent a balloon catheter according to FIGS. 2-4is used, which comprises a stem 13 having three lumen one receiving aguide wire 14 and the other two supplying and draining a liquid, e.g. asalt solution, to and from, respectively, a balloon 15 at one end of thestem. The liquid can be heated and can be supplied under pressure bymeans of a syringe 16 connected to the other end of the stem, FIG. 4.The stent 10 is located on the outside of the balloon when the balloonis collapsed, FIG. 3, and is inserted by means of the balloon catheterin a known manner into a blood vessel. When the stent is positioned atthe intended site in the blood vessel the balloon is put under pressureby pumping liquid, possibly heated, into the balloon under radialexpansion of the stent so that the cover 12 thereof will engage theinside surface of the blood vessel. The stent is of such kind that thisexpansion of the stent provides a permanent change of the shape of thestent so that the stent when the balloon is then collapsed by drainingliquid therefrom and the balloon catheter thereafter is withdrawn fromthe blood vessel will remain in the blood vessel in the manner shown inFIGS. 5 and 6, engaging the inside surface of the wall of the bloodvessel. The stent thus forms a lining in the blood vessel.

The stent is of such kind that it can function as target and receiver ofenergy generated extra-corporeally as ultrasound in order that the stentwill be affected in some way for example in order to develop heat, tovibrate, to change size, to release a substance etc.

According to FIG. 7 the stent 10 is inserted into a coronary vessel andultrasound energy is supplied to the stent from an extra-corporeallylocated ultrasound generator 17. The stent may not or should not bemetallic in this case. It is most favourable if the stent is made of amaterial having an acoustic impedance which is the same as the impedanceof the surrounding tissue (the wall of the vessel) the material of thestent at the same time providing a great attenuation of the ultrasound.All ultrasound from the generator 17 arriving at the stent will passinto the stent, and when the ultrasound is attenuated in the material ofthe stent the ultrasound energy will be converted into heat. There isalso a possibility that the interface between the stent and the tissuewill be heated if the acoustic impedance of the stent and the acousticimpedance of the tissue are slightly different. However, the heatconductivity of the stent in that case must differ from that of thetissue. The effect provided by the ultrasound is dependent of thefrequency of the ultrasound, which also defines the depth in the bodyreached by the ultrasound; higher frequencies provide a shorter range inthe body. It is also possible that the ultrasound consisting of smallvibrations causes vibration of the stent at high frequency.

The ultrasound generator in a known manner, such as that shown in FIG.8, can comprise a number of ultrasound transmitters 18 which are mountedto a spherically concave surface of a carrier or reflector 19 of plasticin order to focus the ultrasound beams emitted by the individualultrasound transmitters to a common point. At the therapeutic treatmentthis point is located on the stent or a position in close juxtapositionof the stent.

The stent either the socket 10 with or without coating, or the cover 11,or both, can be of such nature that some therapeutically activesubstance is released from the stent at heating or vibration. It is alsoconceivable that the stent is of such nature that the radial dimensionthereof will decrease or increase by heating of the stent.

The device according to the invention allows repeated therapeutictreatment of the blood vessel, which preferably is effected during thefirst six weeks after insertion of the stent. By heating of the stent orby imparting vibration to the stent when energy is supplied to the stentextra-corporeally it can be prevented that biologic material growsinside the stent, so called sub-intimal hyperplaci, and that cellsalready formed are removed. Due to the fact that the stent has a heatinsulating cover 12 heat energy developed in the stent will be directedinwards (subintimally) into the stent as indicated by arrows in FIG. 6.Endotel cells will cover the stent and will be present between the bloodand the stent. Without a heat insulating cover or if the cover functionsas receiver of ultrasound energy the heat energy can also be directedoutwards towards media in the blood vessel in order to retard themigration of smooth muscle cells from media to subendotelial position.Two or more stents can be provided mutually spaced in a blood vessel ora system of blood vessels so that the therapeutical effect will beprovided between the stents along a distance of the blood vessel or thesystem of blood vessels, respectively.

The socket 11 can be coated with a composition for slow release of apharmacon which prevents or retards the growth of coating (plaque) onthe inside surface of the socket.

What is claimed is:
 1. Device for therapeutic treatment of a bloodvessel comprising a radially expandable stent a balloon catheter forinsertion of the stent into the blood vessel and expansion thereof toengagement with an inside surface of the blood vessel in order that thestent will be left in the expanded condition thereof as an inside liningin the blood vessel after withdrawal of the balloon catheter from theblood vessel, and means for wireless transmission of energy from anextra-corporal position to the stent at the site thereof in the bloodvessel, engaging the inside surface thereof, wherein said meanscomprises a generator for generating ultrasound energy and that thestent is of such nature that it is brought to vibrate and thereby toheat up when exposed to ultrasound.
 2. Device according to claim 1,characterized in that the stent (11) has an acoustic impedance which issubstantially in agreement with the acoustic impedance of body tissue.3. Device according to claim 1, characterized in that the stentcomprises a socket (11) formed as a netting, axially slotted, or shapedin another way in order to be radially expandable.
 4. Device accordingto claim 3, characterized in that the socket (11) is metallic.
 5. Deviceaccording to claim 3, characterized in that the socket (11) is providedwith a radially expandable coating (12).
 6. Device according to claim 5,characterized in that the coating (12) consists of silicon rubber orgraft.
 7. Device according to claim 6, characterized in that carbonpowder is mixed with the coating (12).
 8. Device according to claim 3,characterized in that the socket consists of plastic.
 9. Deviceaccording to any of claims 1, characterized in that a therapeuticsubstance is contained by the stent said substance being releasable fromthe stent by heating or vibration thereof.
 10. Device according to anyof claims 1, characterized in that the stent is coated with acomposition for slow release of a pharmacon.
 11. Device according to anyof claims 1, characterized in that the generator comprises severalultrasound transmitters mounted to a reflector for concentration of theeffect transmitted therefrom to a collection point on the stent or inthe vicinity thereof.